Fertility rates around the world are declining. Trump supporters won't like the solution.

Falling fertility rates do not immediately have to result in receding population numbers, as migration and better health care also impact overall figures, according to the study

Almost half of all countries have fertility rates below the replacement level, according to an unprecedented study published by The Lancet journal. While there was not a single nation with a fertility rate below the 2.05 threshold back in 1950, the global average is now only 2.4 - down from 4.7 about 70 years ago.Getty Images

Almost half of all countries have fertility rates below the replacement level, according to an unprecedented study published by The Lancet journal. While there was not a single nation with a fertility rate below the 2.05 threshold back in 1950, the global average is now only 2.4 — down from 4.7 about 70 years ago.

Differences between nations have become more pronounced, with some European countries having record-low rates down to one child per woman on average, compared to more than six children in some African nations.

If you live in a poorer nation with high fertility rates, a decrease would likely be a reason for celebration. Lower fertility rates are often the result of fewer child deaths, easily accessible contraception and prosperous economies, which explains why Europe, North America and richer Asian nations like Japan are disproportionately affected.

In countries with below-replacement level fertility rates, however, the costs outweigh the benefits. Europe has struggled with this challenge for years. Even more so than the United States, European welfare largely depends on a sufficient number of working-age residents who can finance health care, pensions and social security for everyone. The fewer there are, the more complicated it becomes to sustain a system that was set up in a century when falling fertility rates were among the problems people had to worry least about.

Alarmed by continuously dropping figures, some EU governments have taken drastic measures. Italy’s Health Ministry launched an ad campaign two years ago to remind people that Sept. 22 was “fertility day.” Other countries have sought to address the issue by focusing on education. In Denmark, for instance, schoolchildren are now taught in class that having babies doesn’t only come with risks, but also with benefits.

But this week’s study raises serious doubts over the impact of such policies or proposals. “Pro-natalist policies have been pursued in more than a dozen countries but the effects on fertility rates have not been large,” they wrote. Instead, they argue, an increasingly large share of the world’s population may have to come to terms with higher retirement ages, slashed benefits and — ironically above all — probably the most divisive issue of this century, so far: migration.

Falling fertility rates do not immediately have to result in receding population numbers, as migration and better health care also impact overall figures, according to the study that was funded by the Bill & Melinda Gates Foundation. While almost half of all nations now have fertility rates below the replacement level, population growth only declined in 33 countries from 2010 to 2017. The countries where population figures remained steady despite lower fertility rates also experienced a higher influx of migrants. The fertility rate in the United States is actually also below replacement levels at 1.8, yet the population is still growing, thanks in large part due to immigration.

Migration has so far saved the United States from following the fate of Europe’s aging societies. But a fall in net migration has already slowed U.S. population growth and could eventually lead to a negative trend. As other global measures to boost fertility rates have so far failed, migration had proven to be “effective in sustaining population numbers,” the authors of the study write.

Based on that analysis, slashing migration numbers – as the Trump administration is attempting to – and operating a budget that relies on a young workforce appears contradictory.

It’s a conclusion that will not sit well among an increasing number of voters in the United States and Europe.